The present disclosure relates to an optical information recording medium. Specifically, the disclosure relates to an optical information recording medium with two or more information signal layers.
The market for optical information recording media has hitherto been led by CDs (Compact Discs), DVDs (Digital Versatile Discs), and the like. However, in recent years, along with the proliferation of high definition television and dramatic increase in data handled by PCs (Personal Computers), there have been demands for further increases in the capacities of optical information recording media. To meet such demands, mass storage optical information recording media that are compatible with blue lasers such as BDs (Blu-ray Discs (registered trademark)) have appeared, and markets for new mass storage information recording media are being established.
Although there are rewritable optical information recording media typified by the CD-RW (Compact Disc-ReWritable) and the DVD±RW (Digital Versatile Disc±ReWritable) and direct read after write type optical information recording media typified by the CD-R (Compact Disc-Recordable) and the DVD-R (Digital Versatile Disc-Recordable) as recordable optical information recording media, the latter in particular have contributed greatly to the expansion of the market as low cost media. Accordingly, with mass storage optical information recording media that are compatible with blue lasers, lowering the cost of direct read after write type optical information recording media is likewise considered important in order to expand the market. Furthermore, it is generally said that compared to hard disk drives (HDD) or flash memories, optical information recording media have high storage reliability due to the recording and reproduction principle thereof, and there is demand for use as archival media, starting to be used for the storage of critical information.
As the recording material that is used in a direct read after write type optical information recording medium, there are inorganic materials and organic pigment materials. Although organic pigment materials have mainly been considered for the recording material of a direct read after write type optical information recording media of the related art, with the mass storage optical information recording media of recent years, inorganic materials are also being widely considered for the recording material.
As one of the inorganic materials that are being widely considered, there is an inorganic material that includes a Pd oxide. For example, an inorganic recording layer that includes In oxide and Pd oxide where the Pd oxide includes Pd monoxide and Pd dioxide and the ratio of Pd atoms with respect to the total of In atoms and Pd atoms is 6 to 60 atomic % is proposed in Japanese Unexamined Patent Application Publication No. 2010-137545. Further, an inorganic recording layer that includes one or both of In and Sn, Pd, and O is proposed in Japanese Unexamined Patent Application Publication No. 2010-218636.
Incidentally, in recent years, in order to further increase the recording capacity in recordable high-density optical information recording media such as DVDs and BDs, techniques for increasing the number of recording layers have been widely adopted. With a multi-layer optical information recording medium, recording and reproduction of information signals with respect to the recording layer positioned at the deepest portion from the information reading face side is performed using laser light that has been transmitted through the recording layer immediately before the recording layer position at the deepest portion. Therefore, with a recording layer other than the recording layer positioned at the deepest portion from the information reading face side, if the transmittances of the information signal layers change greatly before and after the recording of information signals, since the effective laser strength of the recording layer positioned at the deepest portion changes, recording of information signals on the layer at the deepest portion is not performed appropriately. In particular, with an optical information recording medium with three or more layers, since the number of information signal layers that are transmitted increases and the influence of changes in the transmittance which is multiplied with the number of layers with respect to the layer at the deepest portion becomes rather large, the more layers a medium has, the smaller the changes in the transmittance ought to be before and after recording.